To navigate effectively through a complex three-dimensional environment, we must accurately estimate our own motion relative to the objects around us. Perception of self-motion is a multi-modal process, involving ntegration of visual, vestibular, and proprioceptive/somatosensory cues. For example, patterns of image motion across the retina ('optic flow') can be strong cues to self-motion, as evidenced by the fact that optic flow alone can elicit the illusion of self-motion (vection). We propose here to systematically explore a potential contribution of area 2v in the perception of translational and/or rotational self-motion and to directly compare these contributions to those of the ventral intraparietal area (VIP) and the dorsal subdivision of the medial superior temporal (MSTd) areas. Area 2v is one of the so-called 'vestibular' cortical areas with both vestibular and optic flow responsiveness, located in the most anterior and lateral tip of the intraparietal sulcus. Simultaneous behavioral and electrophysiological experiments will be carried out using rhesus monkeys in a state-of-the-art virtual reality apparatus. These studies will combine behavioral, cognitive, and neural analyses to address an important, yet underdeveloped, area of sensory and cognitive neuroscience: the mechanisms of multi-sensory integration underlying self-motion perception. We will be attacking this difficult problem using a combination of single unit recording, electrical microstimulation, inactivation and imaging techniques. Specific aims 1 and 2 will characterize the 3D tuning properties of neurons during optic flow stimulation alone (Visual condition), motion in darkness (Vestibular condition) and Combined combinations of the two cues. In addition, we will also characterize the reference frames of Visual or Vestibular signals. In aim 3, we will test for direct links between area 2v neuronal activity and self-motion perception using a fine motion direction discrimination task. Together, these studies will provide a vital test of the hypothesis that area 2v is part of the neural substrate for self-motion perception. The proposed studies aim at filling an apparent gap in knowledge, important for understanding and treating cognitive deficits of spatial perception.